docs: def publishing_set_update_time(sender, instance, **kwargs):
      """ Update the time modified before saving a publishable object. """
      if hasattr(instance, 'publishing_linked'):
          # Hack to avoid updating `publishing_modified_at` field when a draft
          # publishable item is saved as part of a `publish` operation. This
          # ensures that the `publishing_published_at` timestamp is later than
          # the `publishing_modified_at` timestamp when we publish, which is
          # vital for us to correctly detect whether a draft is "dirty".
          if getattr(instance, '_skip_update_publishing_modified_at', False):
              # Reset flag, in case instance is re-used (e.g. in tests)
              instance._skip_update_publishing_modified_at = False
              return
          instance.publishing_modified_at = timezone.now()